// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System.Collections.Generic;
using Microsoft.AspNetCore.Razor.Language;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace Microsoft.CodeAnalysis.Razor
{
    // Rewrites type names to use the 'global::' prefix for identifiers.
    //
    // This is useful when we're generating code in a different namespace than
    // what the user code lives in. When we synthesize a namespace it's easy to have
    // clashes.
    internal class GlobalQualifiedTypeNameRewriter : TypeNameRewriter
    {
        // List of names to ignore.
        //
        // NOTE: this is the list of type parameters defined on the component.
        private readonly HashSet<string> _ignore;

        public GlobalQualifiedTypeNameRewriter(ICollection<string> ignore)
        {
            _ignore = new HashSet<string>(ignore);
        }

        public override string Rewrite(string typeName)
        {
            var parsed = SyntaxFactory.ParseTypeName(typeName);
            var rewritten = (TypeSyntax)new Visitor(_ignore).Visit(parsed);
            return rewritten.ToFullString();
        }

        private class Visitor : CSharpSyntaxRewriter
        {
            private readonly HashSet<string> _ignore;

            public Visitor(HashSet<string> ignore)
            {
                _ignore = ignore;
            }

            public override SyntaxNode Visit(SyntaxNode node)
            {
                return base.Visit(node);
            }

            public override SyntaxNode VisitQualifiedName(QualifiedNameSyntax node)
            {
                if (node.Parent is QualifiedNameSyntax)
                {
                    return base.VisitQualifiedName(node);
                }

                // Need to rewrite postorder so we can rewrite the names of generic type arguments.
                node = (QualifiedNameSyntax)base.VisitQualifiedName(node);

                // Rewriting these is complicated, best to just tostring and parse again.
                return SyntaxFactory.ParseTypeName("global::" + node.ToString());
            }

            public override SyntaxNode VisitIdentifierName(IdentifierNameSyntax node)
            {
                if (_ignore.Contains(node.ToString()))
                {
                    return node;
                }

                if (node.Parent != null)
                {
                    return node;
                }

                return SyntaxFactory.AliasQualifiedName(SyntaxFactory.IdentifierName(SyntaxFactory.Token(CSharp.SyntaxKind.GlobalKeyword)), node);
            }
        }
    }
}
